Detection apparatus, electric power receiving apparatus, electric power transmission apparatus, wireless electric power transmission system, and detection method

ABSTRACT

A method for wireless power transmission includes obtaining, via a Q-value circuit, first and second voltages at respective first and second nodes of a resonance circuit. The first and second voltages are effective to determine if foreign matter is present in a space affecting wireless power transmission. The method includes controlling a switching section between the Q-value circuit and the resonance circuit such that at least a part of the electric power transmission process occurs at a different time than when the first and second voltages are obtained.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of application Ser. No.15/068,049, filed Mar. 11, 2016, which is a Continuation of applicationSer. No. 13/551,861, filed Jul. 18, 2012, now U.S. Pat. No. 9,467,205,issued Oct. 11, 2016, which claims the benefit of Japanese PriorityPatent Application JP 2011-162589 filed Jul. 25, 2011, the entirecontents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a detection apparatus, an electricpower receiving apparatus, an electric power transmission apparatus, awireless electric power transmission system, and a detection method thatdetect the presence of a conductor, such as a metal.

In recent years, the development of non-contact electric powertransmission systems that supply electric power in a non-contact manner(wireless electric power supply) has been increasingly performed.Methods of realizing wireless electric power supply broadly include twotypes of techniques.

One of the techniques is an already widely used electromagneticinduction method, in which the degree of coupling between the electricpower transmission side and the electric power receiving side is veryhigh, and electric power supply is possible at high efficiency. However,it is necessary to maintain a coupling coefficient between the electricpower transmission side and the electric power receiving side.Consequently, in a case where the electric power transmission side andthe electric power receiving side are spaced apart from each other or ina case where there is a positional displacement, the electric powertransmission efficiency (hereinafter referred to as an “inter-coilefficiency”) between the coil of the electric power transmission sideand the coil of the electric power receiving side is greatlydeteriorated.

The other technique is a technique called a magnetic-field resonancemethod in which a resonance phenomenon is actively used and thus, themagnetic flux shared by the electric power supply source and theelectric power supply destination may be small. In the magnetic-fieldresonance method, even when the coupling coefficient is small, if the Qvalue (Quality factor) is high, inter-coil efficiency does notdeteriorate. The Q value is an index (indicating the strength of theresonance of the resonance circuit) representing the relationshipbetween the retention and the loss of energy of the circuit having thecoil of the electric power transmission side or the electric powerreceiving side. That is, axial alignment between the electric powertransmission side coil and the electric power receiving side coil isunnecessary, and there is advantage that the degree of freedom of theposition and the distance of the electric power transmission side andthe electric power receiving side is high.

In a non-contact or wireless electric power transmission system, animportant element is one for heat generation countermeasures for metalforeign matter. Not limited to the electromagnetic induction method orthe magnetic-field resonance method, when electric power supply is to beperformed in a non-contact manner, in the case where a metal is presentbetween the electric power transmission side and the electric powerreceiving side, an eddy current is generated, and there is a risk thatthe metal will generate heat. In order to reduce this heat generation,many techniques for detecting metal foreign matter have been proposed.For example, a technique using a light sensor or a temperature sensor ispopular. However, in the detection method using a sensor, costs areincurred in a case where the electric power supply range is wide as inthe magnetic-field resonance method. Furthermore, in the case of, forexample, a temperature sensor, since the output result of thetemperature sensor depends on the thermal conductivity in thesurroundings thereof, design restrictions are imposed on the devices onthe transmission side and on the reception side.

Therefore, a technique has been proposed in which the presence orabsence of metal foreign matter is determined by observing a change inparameters (electric current, voltage, etc.) when metal foreign matterenters the space between the electric power transmission side and theelectric power receiving side. With such a technique, it is notnecessary to impose design restrictions, and costs can be reduced. Forexample, in Japanese Unexamined Patent Application Publication No.2008-206231, a method of detecting metal foreign matter by using thedegree of modulation at the time of communication between an electricpower transmission side and an electric power receiving side has beenproposed. In Japanese Unexamined Patent Application Publication No.2001-275280, a method (foreign matter detection by DC-DC efficiency) ofdetecting metal foreign matter using eddy current loss has beenproposed.

SUMMARY

However, in the techniques proposed by the Japanese Unexamined PatentApplication Publication Nos. 2008-206231 and 2001-275280, the influenceof the metal housing on the electric power receiving side is not takeninto consideration. In a case where charging of a typical portabledevice is considered, there is a high probability that some sort ofmetal (metal housing, metal parts, etc.) is used in the portable deviceand thus, distinction of whether a change in the parameter is caused bythe “influence of a metal housing or the like” or by a “mixture of metalforeign matter” is difficult. When Japanese Unexamined PatentApplication Publication No. 2001-275280 is used as an example, it isdifficult to determine whether the eddy current loss is generated in themetal housing of the portable device or the eddy current loss isgenerated as a result of metal foreign matter being mixed in between theelectric power transmission side and the electric power receiving side.As described above, it is difficult to say that the techniques that havebeen proposed in Japanese Unexamined Patent Application Publication Nos.2008-206231 and 2001-275280 are able to detect metal foreign matter withhigh accuracy.

It is desirable to improve the accuracy of the detection of metalforeign matter, which is present between an electric power transmissionside and an electric power receiving side.

In an embodiment of the present disclosure, at the time of measurementof a Q value, the circuit configuration of a resonance circuit includingat least an inductor (e.g., coil) and a capacitor, which are included inan electric power transmission apparatus or an electric power receivingapparatus constituting a wireless (or non-contact) electric powertransmission system, is switched from the circuit configuration at thetime of electric power supply, so that the electrostatic capacitancevalue of the electrostatic capacitance components parallel to the coilis increased. Then, after the circuit configuration is switched, the Qvalue of the resonance circuit is measured.

According to the embodiment of the present disclosure, the electrostaticcapacitance value of the electrostatic capacitance components parallelto the coil increases, and the impedance of the resonance circuitincreases. As a result, the amplitude level of the voltage that isdetected from the resonance circuit at the time of the measurement ofthe Q value increases, and the SN ratio of the Q value of the resonancecircuit is improved.

According to the present disclosure, by individually configuring theresonance circuit at the time of electric power supply and the resonancecircuit at the time of detection of metal foreign matter by the Q valuemeasurement most appropriately, it is possible to improve the accuracyof the detection of metal foreign matter without deteriorating electricpower supply performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating an example of the relationship betweenfrequency and a Q value;

FIG. 2 is a graph in which a Q value is compared for each frequency in acase where metal foreign matter is present and in a case where metalforeign matter is not present;

FIG. 3 is a graph illustrating the relationship between frequency andthe amount of change in a Q value in a case where metal foreign matterpresent and in a case where metal foreign matter is not present;

FIG. 4 is a circuit diagram illustrating an overview of an electricpower transmission apparatus used for a wireless or non-contact electricpower transmission system;

FIG. 5 is a block diagram illustrating an example of the internalconfiguration of an electric power transmission apparatus (primary side)used for a wireless non-contact electric power transmission system;

FIG. 6 is a block diagram illustrating an example of the internalconfiguration of a batteryless electric power receiving apparatus(secondary side) used for a wireless or non-contact electric powertransmission system;

FIG. 7 is an illustration of the concept of voltage division in anequivalent circuit for which a series resonance circuit is assumed;

FIG. 8 is a waveform chart illustrating an example of voltage signalsthat are observed at specified spots of the equivalent circuit shown inFIG. 7;

FIGS. 9A, 9B, and 9C are circuit diagrams illustrating theconfigurations of different resonance circuits;

FIG. 10 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9A;

FIG. 11 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9B;

FIG. 12 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9C;

FIG. 13 depicts a method of calculating the impedance value of aresonance circuit by using a transfer function;

FIG. 14 is an example of a graph illustrating the relationship between acoupling coefficient and impedance;

FIGS. 15A, 15B, and 15C are circuit diagrams of connection examples ofcapacitors for the coils of the resonance circuits;

FIG. 16 is a block diagram illustrating the main portion of an exampleof the internal configuration of an electric power receiving apparatus(secondary side) according to a first exemplary embodiment of thepresent disclosure;

FIG. 17 is a flowchart illustrating processing at the time of electricpower supply of a wireless or non-contact electric power transmissionsystem according to a first exemplary embodiment of the disclosure;

FIG. 18 is a flowchart illustrating processing in a case where a Q valuecalculation is to be performed, in which frequency sweep is reflected,in the primary side (electric power transmission apparatus);

FIG. 19 is an operation timing chart of a wireless or non-contactelectric power transmission system according to the first exemplaryembodiment of the disclosure;

FIG. 20 is a graph illustrating an example of the relationship between aplurality of frequencies and Q values in a resonance circuit;

FIG. 21 is a flowchart illustrating processing in a case where a Q valuecalculation is performed in the primary side (electric powertransmission apparatus);

FIG. 22 is a block diagram illustrating the main portion of an exampleof the internal configuration of an electric power transmissionapparatus (primary side) according to a second exemplary embodiment ofthe present disclosure;

FIG. 23 is an equivalent circuit diagram illustrating the configurationof a resonance circuit when a third switch of the electric powertransmission apparatus (primary side) shown in FIG. 22 is turned on andoff;

FIG. 24 is a graph illustrating frequency characteristics of impedancein a series resonance circuit;

FIG. 25 is a graph illustrating frequency characteristics of impedancein a parallel resonance circuit; and

FIG. 26 is a circuit diagram for calculating a Q value on the basis ofthe ratio of real part components and imaginary part components ofimpedance according to a third exemplary embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below withreference to the attached drawings. In the present disclosure and thedrawings, components having substantially the same functions orconfiguration are designated with the same reference numerals, andduplicate descriptions thereof are omitted.

The description will be given in the following order.

1. First Embodiment (circuit switching unit: example in whichelectrostatic capacitance value of capacitor is switched betweenelectric power supply time and Q value measurement time on electricpower receiving side) 2. Second Embodiment (circuit switching unit:example in which electrostatic capacitance value of capacitor isswitched between electric power supply time and Q value measurement timeon electric power transmission side) 3. Others (Q value measurementcircuit: modification of Q value measurement process)

1. First Embodiment Introductory Description

The technology for detecting metal foreign matter in the presentdisclosure is a technique of detecting metal foreign matter by using achange in Q value described above. The Q value is an index indicatingthe relationship between the retention and the loss of energy, and isgenerally used as a value indicating the acuteness (strength ofresonance) of the peak of the resonance of a resonance circuit. The termmetal foreign matter refers to a conductor, such as a metal, which ispresent between the electric power transmission side (primary side) andthe electric power receiving side (secondary side), and the conductorincludes conductors in a wide sense, which may include, for example,semiconductors.

However, in this technique, it is necessary that the adjustment of aresonance point (resonance frequency) be performed at a place having acertain Q value. For this reason, in a case where electric power supplyis performed using an alternating-current signal of a frequency having alow Q value as in a typical electromagnetic induction method, theabsolute value of the Q value is low and thus, detection accuracy isdeteriorated. Therefore, care should be exercised regarding such usage.

FIG. 1 illustrates an example of the relationship between frequency anda Q value associated with a coil.

The configuration of the coil used for measurements has 8 turns havingan outer shape of 30.times.40 mm and an inner diameter of 20.times.30mm. As shown in FIG. 1, the Q value indicated by a Q value frequencycharacteristic curve 1 markedly changes with the frequency. If this coilis used for electric power supply at 100 kHz (resonance is made bycapacitor), the absolute value of the Q value becomes about 50, and theQ value becomes approximately half or less in comparison with thefrequency of the maximum value.

FIG. 2 is a graph in which a Q value is compared for each frequency in acase where metal foreign matter is present (e.g., mixed in with a coil)and in a case where the metal foreign matter is not present (e.g., notmixed in with the coil).

In this example, a Q value when a 15-mm square of iron was placed asmetal foreign matter in the center of the coil was measured. It can beseen from FIG. 2 that at a frequency with a higher Q value, thedifference between a Q value frequency characteristic curve 2 when metalforeign matter is present (e.g., mixed in) and the Q value frequencycharacteristic curve 1 when the metal foreign matter is not present(e.g., not mixed) is greater.

FIG. 3 is a graph illustrating the relationship between frequency andthe amount of change in a Q value in a case where metal foreign matteris mixed in and in a case where metal foreign matter is not mixed in.This shows the difference in Q value for each frequency, shown in FIG.2, as a relative value.

It can be seen from FIG. 3 that the change in the Q value is markedlyaffected by the frequency, and it can be seen from FIGS. 2 and 3 thatfor a frequency at which the absolute value of the Q value is larger,the change in the Q value is larger. That is, by detecting metal foreignmatter by using a frequency having a large absolute value of the Qvalue, the accuracy of detection of metal foreign matter is improved.

Principles of Q Value Measurement

Here, a description will be given, with reference to FIG. 4, of theprinciples of Q value measurement.

FIG. 4 is a circuit diagram illustrating an overview of an electricpower transmission apparatus used for a non-contact electric powertransmission system. The circuit of an electric power transmissionapparatus 10 shown in FIG. 4 is an example of the most basic circuitconfiguration (in the case of magnetic field coupling) representing theprinciples of measurement of a Q value. Although a circuit including aseries resonance circuit is illustrated, various detailed exemplaryconfigurations can be considered as long as the function of theresonance circuit is included. The Q value measurement of the resonancecircuit is a technique that is also used for a measuring instrument (LCRmeter). Although an example of the resonance circuit of the electricpower transmission apparatus (primary side) is illustrated, themeasurement principles can be applied in the same way to the resonancecircuit of the electric power receiving apparatus (secondary side).

For example, if there is a metal piece acting as metal foreign matternear the primary side coil 15 of the electric power transmissionapparatus 10, a magnetic line passes through the metal piece, and aneddy current is generated in the metal piece. When viewed from theprimary side coil 15, this appears that the metal piece and the primaryside coil 15 are electromagnetically coupled with each other, and a realresistance load is added to the primary side coil 15, causing the Qvalue of the primary side to be changed. The measurement of the Q valueleads to the detection of the metal foreign matter (electromagneticallycoupled state) near the primary side coil 15.

The electric power transmission apparatus 10 includes a signal source 11including an AC power supply 12 for generating an alternating-currentsignal (sine wave) and a resistance element 13, a capacitor 14, and aprimary side coil 15 (electric power transmission coil, an example of acoil). The resistance element 13 is a schematic representation of theinternal resistance (output impedance) of the AC power supply 12. Thecapacitor 14 and the primary side coil 15 are connected to the signalsource 11 in such a manner as to form a series resonance circuit (anexample of resonance circuit). Then, in order that resonance is made ata frequency desired to be measured, the value (C value) of thecapacitance of the capacitor 14 and the value (L value) of theinductance of the primary side coil 15 are adjusted. The electric powertransmission unit including the signal source 11 and the capacitor 14transmits electric power to the outside through the primary side coil 15by using a load modulation method in a wireless or non-contact manner.

When the voltage between the primary side coil 15 and the capacitor 14forming the series resonance circuit is denoted as V1 (an example ofvoltage applied to the resonance circuit) and the voltage across theprimary side coil 15 is denoted as V2, the Q value of the seriesresonance circuit is represented by Equation (1).

Q=V2V1=2·pi·fLrs(1)  ##EQU00001##

where r.sub.s is the effective resistance value at frequency f

The voltage V1 is multiplied by Q, and the voltage V2 is obtained. Whenthe metal piece approaches the primary side coil 15, the effectiveresistance value r.sub.s increases, and the Q value decreases. Asdescribed above, when the metal piece approaches the primary side coil15, the Q value (electromagnetically coupled state) to be measuredchanges. Consequently, by detecting this change, it is possible todetect the metal piece near the primary side coil 15.

Example of Configuration of a Wireless or Non-Contact Electric PowerTransmission System Example of Configuration of Electric PowerTransmission Apparatus

FIG. 5 is a block diagram illustrating an example of the internalconfiguration of the electric power transmission apparatus (primaryside) used for a non-contact electric power transmission system. Theblock diagram shown in FIG. 5 illustrates a more specific configurationof the electric power transmission apparatus shown in FIG. 4, in which aQ value measurement circuit 20 (an example of a detection unit) shown inFIG. 5 detects metal foreign matter. The electric power transmissionapparatus in which the Q value measurement circuit 20 is provided is anexample of a detection apparatus.

As an example, elements forming the Q value measurement circuit 20include rectifying units 21A and 21B, analog-to-digital converters(hereinafter referred to as “ADC”) 22A and 22B, and a main control unit23. Each block forming the electric power transmission apparatus 10including blocks in the Q value measurement circuit 20 operates on thebasis of the electric power supplied from the signal source 11 or abattery (not shown).

The rectifying unit 21A converts an alternating-current signal (ACvoltage) input from between the primary side coil 15 and the capacitor14 into a DC signal (DC voltage), and outputs it. Similarly, therectifying unit 21B converts an alternating-current signal (AC voltage)input from between the signal source 11 and the capacitor 5 into a DCsignal (DC voltage). The converted DC signals are input to thecorresponding ADCs 22A and 22B.

The ADCs 22A and 22B convert analog DC signals input from the rectifyingunits 21A and 21B into digital DC signals, respectively, and output themto the main control unit 23.

The main control unit 23 is an example of the control unit, and controlsthe whole of the electric power transmission apparatus 10 constitutedby, for example, a micro-processing unit (MPU). The main control unit 23functions as a computation processing unit 23A and a determination unit23B.

The computation processing unit 23A is a block for performing apredetermined computation process. In this example, the ratio of thevoltage V1 to the voltage V2, that is, the Q value, is calculated on thebasis of the DC signals that are input from the ADCs 22A and 22B, andthe calculation result is output to the determination unit 23B.Furthermore, the computation processing unit 23A can also obtain theinformation (the physical quantity, such as a voltage value) relating tothe detection of metal foreign matter from the electric power receivingside (secondary side) and can calculate the Q value of the secondaryside on the basis of the information.

The determination unit 23B compares the calculation result input fromthe computation processing unit 23A with a threshold value stored in anon-volatile memory 24, and determines whether or not metal foreignmatter is present nearby on the basis of the comparison result.Furthermore, the determination unit 23B can compare the Q value on theelectric power receiving side with the threshold value so as todetermine whether or not metal foreign matter is present nearby.

The memory 24 stores the threshold value (Ref_Q1) of the primary side Qvalue, which has been measured in advance, in a state in which there wasnothing in the vicinity of the secondary side coil or nothing was placedin the secondary side coil. Furthermore, the memory 24 also stores thethreshold value (Q_Max) of the secondary side Q value obtained from theelectric power receiving side (secondary side).

The communication control unit 25 is an example of the primary sidecommunication unit, and performs communication with the communicationcontrol unit of the electric power receiving apparatus (to be describedlater). For example, the communication control unit 25 performstransmission and reception of information relating to the detection ofmetal foreign matter, such as receiving the Q value, the voltage V1, thevoltage V2 and the like of the resonance circuit including the secondaryside coil of the electric power receiving apparatus. Furthermore, thecommunication control unit 25 instructs the signal source 11 to generateor stop an AC voltage under the control of the main control unit 23. Forthe communication standard in the communication with the electric powerreceiving apparatus, for example, a wireless LAN of IEEE 802.11 standardor Bluetooth (registered trademark) can be used. The configuration maybe formed in such a way that information is transmitted through theprimary side coil 15 and the secondary side coil of the electric powerreceiving apparatus. Furthermore, an instruction may be directly givenfrom the main control unit 23 to the signal source 11 without using thecommunication control unit 25.

The input unit 26 generates an input signal corresponding to a useroperation and outputs the input signal to the main control unit 23.

In this example, the configuration has been described as having the Qvalue measurement circuit 20 incorporated in the electric powertransmission apparatus 10 and as being capable of detecting metalforeign matter on the basis of the Q value on the primary side and themetal foreign matter on the basis of the Q value on the secondary side.Not limited to this, it is sufficient that the electric powertransmission apparatus 10 includes a main control unit 23 that performsat least a computation process and a determination process, and acommunication control unit 25, and includes a function of determiningthe electromagnetically coupled state on the basis of the Q value of theelectric power receiving apparatus and detecting metal foreign matter.

As described above, by applying the measurement principles to anelectric power receiving apparatus (secondary side), it is possible forthe electric power receiving apparatus to measure the Q value. However,while electric power supply is being performed at the time of Q valuemeasurement, the magnetic field output from the electric powertransmission side causes large electric power to be generated in thecoil of the electric power receiving apparatus, and the voltage V2 isdifficult to be measured normally. For this reason, an accurate Q valueis difficult to be obtained, and there is a risk that metal foreignmatter is difficult to be detected with high accuracy.

In order to solve the inconvenience, it is necessary to stop electricpower supply at the time of measurement. However, if electric powersupply is stopped, a large battery that operates the circuit formeasuring the Q value on the secondary side becomes necessary. If abattery is housed in the electric power receiving apparatus, an adverseinfluence may occur in the product service lifetime, and a situation mayoccur in which, for example, metal foreign matter detection is difficultto be performed in a case where the charged capacitance of the batteryof the portable device becomes exhausted, and charging is desired to beperformed immediately.

Accordingly, the inventors of the present disclosure considered abatteryless electromagnetically coupled state detection technology inwhich when Q value measurement is to be performed on the secondary sideby using electric power supplied from the primary side, first, while theelectric power reception is being performed from the primary side, the Qvalue measurement is not performed on the secondary side.

Example of Configuration of Electric Power Receiving Apparatus

An example of the configuration of a batteryless electric powerreceiving apparatus (secondary side), which is used for a non-contactelectric power transmission system, will be described below.

FIG. 6 is a block diagram illustrating an example of the internalconfiguration of an electric power receiving apparatus that is appliedto a portable device or the like. The configuration is formed in such away that a circuit used at the time of electric power supply and at thetime of Q value measurement is switched between by switching. At thetime of Q value measurement, a Q value measurement circuit 60 (anexample of detection unit) detects whether metal foreign matter ispresent. The electric power receiving apparatus provided with the Qvalue measurement circuit 60 is an example of the detection apparatus.

The electric power receiving apparatus 30 of the present exampleincludes a secondary side coil 31 and a capacitor 32 that is connectedin parallel to the secondary side coil 31. One end of theparallel-connected secondary side coil 31 and one end of the capacitor32 are connected to one end of the capacitor 33, and the other end ofthe capacitor 33 is connected to one input end of the rectifying unit34. The other ends of the secondary side coil 31 and the capacitor 32,which are connected in parallel with each other, are connected to theother input end of the rectifying unit 34. One output end of therectifying unit 34 is connected to the input end of the first regulator36 through a second switch 39, the output end of the first regulator 36is connected to the load, and the other output end of the rectifyingunit 34 is connected to the ground terminal. A second regulator 37 isalso connected to one output end of the rectifying unit 34. Furthermore,the capacitor 35 and the first switch 38 are connected in series witheach other, one end of the capacitor 35 is connected to one output endof the rectifying unit 34, and one end of the first switch 38 isconnected to the other output end of the rectifying unit 34.

The first regulator 36 performs control so that the voltage and theelectric current to be output are typically maintained constant, andsupplies a voltage of 5V to the load, for example. Similarly, the secondregulator 37 supplies a voltage of 3V to each block including eachswitch, for example.

A third switch 40 is connected to the other end of the capacitor 33, andis connected to an AC power supply 50 (oscillation circuit) through thethird switch 40, a resistance element 52, and an amplifier 51.Furthermore, the input end of the amplifier 44A is connected to theother end of the capacitor 33 through a third switch 41. Additionally,the input end of the amplifier 44B is connected to one end of thecapacitor 33 through a third switch 42. Furthermore, the other ends ofthe secondary side coil 31 and the capacitor 32, which are connected inparallel with each other, are connected to the ground terminal throughthe third switch 43.

For the first switch 38 (an example of first switching unit), the secondswitch 39 (an example of second switching unit), and the third switches40 to 43 (examples of third switching units), switching elements, suchas transistors and MOSFETs, are used. In this example, MOSFETs are used.

As this example, components forming the Q value measurement circuit 60include amplifiers 44A and 44B, envelope detection units 45A and 45B ata subsequent stage, analog-to-digital converters (hereinafter referredto as “ADC”) 46A and 46B, and a main control unit 47 (computationprocessing unit 47A, determination unit 47B).

The output end of the amplifier 44A is connected to an envelopedetection unit 45A. The envelope detection unit 45A detects the envelopeof the alternating-current signal (corresponding to the voltage V1),which is input from the other end of the capacitor 33 through the thirdswitch 41 and the amplifier 44A, and supplies the detection signal tothe ADC 46A.

Additionally, the output end of the amplifier 44B is connected to anenvelope detection unit 45B. The envelope detection unit 45B detects theenvelope of the alternating-current signal (corresponding to the voltageV2), which is input from one end of the capacitor 33 through the thirdswitch 42 and the amplifier 44B, and supplies the detection signal tothe ADC 46B.

The ADCs 46A and 46B convert analog detection signals input from theenvelope detection units 45A and 45B into digital detection signals,respectively, and output them to the main control unit 47.

The main control unit 47 is an example of the control unit, and controlsthe whole of the electric power receiving apparatus 30 constituted by,for example, a micro-processing unit (MPU). The main control unit 47functions as a computation processing unit 47A and a determination unit47B. The main control unit 47 supplies a driving signal to each switch(a gate terminal of a MOSFET) by using electric power supplied from thesecond regulator 37 so as to control on/off (switch switching function).

The computation processing unit 47A is a block for performing apredetermined computation process, calculates the ratio of the voltageV1 to the voltage V2, that is, Q value, on the basis of the detectionsignal input from the ADCs 46A and 46B, and outputs the calculationresult to the determination unit 47B. Furthermore, the computationprocessing unit 47A can also transmit the information (voltage value,etc.) on the input detection signal to the electric power transmissionside (primary side) in accordance with the setting. Furthermore, at thetime of a metal foreign matter detection process, a frequency sweepprocess is performed (sweep processing function).

The determination unit 47B compares the Q value input from thecomputation processing unit 47A with the threshold value stored in anon-volatile memory 48, and determines whether or not metal foreignmatter is present near on the basis of the comparison result. As will bedescribed later, it is also possible to transmit the measuredinformation to the electric power transmission apparatus 10, so that theelectric power transmission apparatus 10 can calculate the secondaryside Q value and determine the presence or absence of metal foreignmatter.

The memory 48 stores a threshold value to be compared with a Q value,which has been measured in advance, in a state in which there wasnothing in the vicinity of the secondary side coil 31 or nothing wasplaced in the secondary side coil 31.

The communication control unit 49 is an example of the secondary sidecommunication unit, and performs communication with the communicationcontrol unit 25 of the electric power transmission apparatus 10. Forexample, the communication control unit 49 performs transmission andreception of information relating to the detection of the metal foreignmatter, such as transmitting the Q value, the voltage V1, the voltageV2, and the like of the resonance circuit including the secondary sidecoil 31 of the electric power receiving apparatus 30. The communicationstandard applied to the communication control unit 49 is the same as thecommunication standard that is applied to the communication control unit25 of the electric power transmission apparatus 10. The configurationmay be formed in such a way that information is transmitted through thesecondary side coil 31 and the primary side coil 15 of the electricpower transmission apparatus 10.

The AC power supply 50 causes an AC voltage (sine wave) to be generatedat the time of Q value measurement on the basis of the control signal ofthe main control unit 47, and supplies the AC voltage to the other endof the capacitor 33 through the amplifier 51 and the resistance element52.

The input unit 53 generates an input signal corresponding to a useroperation and outputs it to the main control unit 47.

The Q value measurement circuit 60 of the electric power receivingapparatus 30, which is constituted in the manner described above, iscontrolled by the switching of on/off, a group of three switches, thatis, the first switch 38, the second switch 39, and the third switches 40to 43. Hereinafter, the operation of the electric power receivingapparatus 30 will be described by paying attention to switching of theswitches.

First, the electric power received from the electric power transmissionapparatus 10 by the secondary side coil 31 is charged in the capacitor35 (an example of a power storage unit) provided at a subsequent stageof the rectifying unit 34. The electric current value and the time atwhich the electric power transmission apparatus 10 can operate with theelectric power charged in the capacitor is determined by CV=it,

where C denotes the electrostatic capacitance of the capacitor, Vdenotes the voltage value of the capacitor, i denotes the electriccurrent value of the capacitor, and t denotes a time period. That is,when the voltage value charged in a capacitor of 10.mu.F changes from 9Vto 4V, the electric current of 50 mA can be made to flow for 1 msec. Ifthe electrostatic capacitance value of the capacitor is large, largerelectric current can be made to flow or the time period during whichelectric current is made to flow can be extended.

However, if the capacitor 35 having a large electrostatic capacitancevalue is placed at a subsequent stage of the rectifying unit 34, aproblem is considered to occur at the time of communication between theelectric power receiving apparatus 30 and the external device. Thus, itis preferable that control be performed using the first switch 38. Thatis, the drain-source of the first switch 38 is made to conduct at onlythe Q value measurement, and by connecting the capacitor 35, the adverseinfluence is eliminated.

If the consumption of electric current of the Q value measurementcircuit 60 is small to a certain degree and the time period of the Qvalue measurement is short, it is possible to measure the Q value whilethe carrier signal from the electric power transmission apparatus 10 isstopped. When the carrier signal to be output from the electric powertransmission apparatus 10 is to be stopped (at the time of Q valuemeasurement), it is necessary to reliably electrically disconnect theload from the Q value measurement circuit 60. For example, a P-channelMOSFET is used for the second switch 39, so that control of becoming offwhen a carrier signal is input to the electric power receiving apparatus30 may be performed, or control may be performed by using the enablefunction of the first regulator 36. When the capacitor 35 is beingcharged or communication is being performed through the communicationcontrol unit 49 other than the above, there is no problem even if theload is not disconnected from the Q value measurement circuit 60.

At the time of Q value measurement, similarly to the technique of theabove-mentioned measuring instrument (LCR meter), the voltage valueacross the capacitor 33 is measured. Specifically, the third switches 40to 43 are turned on at the time at which the carrier signal is stopped,and the Q value is calculated on the basis of two voltage waveforms thatare detected at one end and the other end of the capacitor 33 throughwhich the sine wave output from the AC power supply 50 is rectified. Bycomparing the calculated Q value with the preset threshold value,detection of metal foreign matter is performed.

Deterioration of SN Ratio at Time of Q Value Measurement

The accuracy of the Q value measurement is also greatly affected by theimpedance value at the resonance point (resonance frequency) of theresonance circuit. As described in the foregoing, in the configurationof the electric power receiving apparatus 30, the circuits at the timeof electric power supply and at the time of Q value measurement areswitched between by switching. That is, the voltage across the capacitor33 is divided by the on-resistance quantity of the third switch 41 andthe impedance at the resonance point of the secondary side coil 31, andthe amplitude of the voltage decreases. For this reason, the voltagedivision ratio increases depending on the impedance at the resonancepoint of the secondary side coil 31, and the SN ratio at the time of Qvalue measurement may deteriorate.

FIG. 7 illustrates the concept of a voltage division in an equivalentcircuit for which a series resonance circuit is assumed. FIG. 8illustrates trial calculation results of a voltage waveform at each spotof the equivalent circuit of FIG. 7.

In FIG. 7, Z1 indicated by the dashed line represents the on-resistancequantity (on-resistance component R1) of the switching element.Furthermore, Z2 indicated by the dashed line represents a seriesresonance circuit as an equivalent circuit formed of a coil L1, acapacitor C1, and the effective resistance configuration (effectiveresistance component r1) at the frequency f of an AC voltage of the ACpower supply E.

In the series resonance circuit, since the impedance at the resonancepoint is formed of only the pure resistance quantity of the coil L1,impedance is voltage-divided at the spot of V1-1 and the spot of V1-2(corresponding to V1 of FIG. 6), shown in FIG. 7, and the amplitude ofthe AC voltage decreases.

The results in which the amplitude of the AC voltage were calculatedactually at the spot of V1-1 and at the spot of V1-2 by simulation areshown in the waveform chart of FIG. 8. The conditions used for the trialcalculation are: the frequency of the AC voltage is 90 kHz, theamplitude is 0.1V, the self-inductance of the coil L1 of the seriesresonance circuit is 14.3.mu.H, the resistance value of the effectiveresistance component r1 is 0.6.OMEGA., the electrostatic capacitancevalue of the capacitor C1 is 227 nF, and the resistance value of theon-resistance component R1 is 3.OMEGA.

In FIG. 8, the waveform of a large amplitude shows the level of the spotV1-1, and the waveform of a small amplitude shows the level at the spotV1-2. It can be certainly seen from this voltage waveform that theamplitude of the AC voltage is decreased.

Next, a description will be given of that the impedance at the resonancepoint of the resonance circuit differs depending on the configuration ofthe resonance circuit.

FIGS. 9A, 9B, and 9C are circuit diagrams illustrating theconfigurations of mutually different resonance circuits.

The resonance circuit of FIG. 9A is a series resonance circuit. Incomparison, the resonance circuit of FIG. 9B has a capacitor C1′, whichis connected in series to the coil L1, and a capacitor C2′, which isconnected in parallel to the coil L1. The resonance circuit of FIG. 9Chas a C1″, which is connected in series to the coil L1, and a C2″ whichis connected in parallel to the coil L1.

In the resonance circuits of FIGS. 9A to 9C, similarly to the case ofFIG. 8, the frequency of the AC voltage is 90 kHz, the amplitude thereofis 0.1V, the self-inductance of the coil L1 is 14.3.mu.H, the resistancevalue of the effective resistance component r1 is 0.6.OMEGA., and theresistance value of the on-resistance component R1 is 3.OMEGA. However,the electrostatic capacitance value of the capacitor C1 of FIG. 9A is227 nF, the electrostatic capacitance value of the capacitors C1′ andC2′ of FIG. 9B are 168 nF and 59 nF, respectively, and the electrostaticcapacitance values of the capacitors C1″ and C2″ of FIG. 9C are 113 nFand 113 nF, respectively.

FIG. 10 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9A.

FIG. 11 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9B.

FIG. 12 is a graph illustrating frequency characteristics of theimpedance of the resonance circuit shown in FIG. 9C.

It can be seen from FIGS. 10 to 12 that the impedance value of theresonance circuit differs even if the resonance frequency (90 kHz inthis example) is the same depending on the constant of the resonancecircuit. In FIG. 10, the impedance value is about 0.6.OMEGA.; in FIG.11, the impedance value is about 1.1.OMEGA.; and in FIG. 12, theimpedance value is about 2.4.OMEGA. The greater the electrostaticcapacitance value of the capacitor that is connected in parallel to thecoil L1, the greater the impedance value at the resonance point.

FIG. 13 is a circuit diagram illustrating a method of calculating theimpedance value of the resonance circuit by using a transfer function bya computer. The circuit example shown in FIG. 13 has the same circuitconfiguration as the equivalent circuit of the resonance circuit shownin FIGS. 9A and 9B.

Referring to FIG. 13, the impedances of Z1 to Z3 indicated using thedashed lines are:

Z1=1j.omega.C1(2)Z2=1j.omega.C2(3)Z3=j.omega.L+R(4)  ##EQU00002##

Here, since Z4 is

Z4=11Z2+1Z3(5)Z4=11j.omega.L+R+j.omega.C2(6)  ##EQU00003##

Therefore, since the whole impedance, Z5, is Z5=Z1+Z4,

Z5=1j.omega.C1+11j.omega.L+R+j.omega.C2,(7)  ##EQU00004##

and when this is simplified, the following is obtained.

Z5=−(C1+C2)jL.omega.2+(C1+C2)R.omega.−jLC1C2.omega.3−jRC1C2.omega.2−C1.omega.(8)  ##EQU00005##

By obtaining the impedance of the point (resonance point) at which theimaginary part becomes 0 in accordance with Equation (8), the simulationresult of the resonance circuit of FIG. 13 can be obtained.

However, at the time of electric power supply, when the electrostaticcapacitance value of the capacitor that is connected in parallel to thecoil of the resonance circuit increases, the impedance value on thesecondary side at the time of electric power supply becomes high,presenting a problem in that the voltage applied across the secondaryside load increases.

The optimal impedance value for the efficiency between the primary sidecoil and the secondary side coil at the time of electric power supply isdetermined by the self-inductance, the Q value, and the couplingcoefficient of the coil. As an example, FIG. 14 illustrates therelationship between a coupling coefficient and impedance.

When the foregoing is considered, if the coil size, the inter-coildistance between the primary side and the secondary side is determinedto a certain degree, and furthermore if the target impedance value ofthe secondary side is determined, the connection form of the capacitor,that is, the configuration and the constant of the resonance circuit,are automatically determined.

FIGS. 15A, 15B, and 15C are circuit diagrams illustrating examples ofconnection forms of capacitors with respect to the coils of resonancecircuits.

There are three types of connection forms of capacitors with respect tothe coil of the resonance circuit:

(1) Series connection to coil (FIG. 15A), (2) Series connection afterparallel connection to coil (FIG. 15B), and (3) Parallel connection tocoil (FIG. 15C), and any circuit configuration can be taken depending onthe case.

The impedance at the resonance point at the time of Q value detectionhas the same value as that when the coupling coefficient of the graphshown in FIG. 12 is 0. At the time of the above (1), the impedance is aminimum value; at the time of the above (3), the impedance is a maximumvalue; and at the time of the above (2), the impedance is a valueintermediate between them.

Therefore, there is a problem in that the optimum configuration of theresonance circuit at the time of electric power supply and the optimumconfiguration of the resonance circuit at the time of Q valuemeasurement do not necessarily match each other.

Example of Configuration of First Embodiment Example of Configuration ofCapacitor and Switch

Accordingly, a technique of switching the configuration (constant) ofthe resonance circuit at the time of electric power supply and at thetime of foreign matter detection by Q value measurement is proposed.

FIG. 16 is a block diagram illustrating the main portion of an exampleof the internal configuration of an electric power receiving apparatus(secondary side) that performs the switching of the configuration(constant) of the resonance circuit at the time of electric power supplyand at the time of Q value measurement according to the first exemplaryembodiment of the present disclosure.

The difference of the electric power receiving apparatus 30A accordingto the present embodiment from the electric power receiving apparatus 30shown in FIG. 6 is that a capacitor 32′ and a capacitor 33′ are added tothe resonance circuit, a third switch 43′ is added thereto, and theremainder is the same as that of FIG. 6. FIG. 6 can therefore bereferenced, as applicable, with respect to these similarities. The thirdswitches 40 to 43, and 43′ are in a state of off at the time of electricpower supply, and are seen as being open and thus, there is no concernthat an adverse influence being exerted at the time of electric powersupply.

The capacitor 32′ is connected in parallel with the capacitor 32. Thecapacitor 33′ is connected in series with the capacitor 33 when thethird switches 40 and 41 are turned on. The third switch 43′ for which atransistor, an MOSFET, or the like is applied is connected between thecapacitor 32′ and the ground terminal. The third switches 41 and 43′ areexamples of circuit switching units.

The switches of the third switches are simultaneously turned on at thetime of Q value measurement. The capacitor 32′ is in parallel to thecapacitor 32, increases the electrostatic capacitance value parallel tothe secondary side coil 31 by turning on the third switch 43 at the timeof Q value measurement, and increase the impedance at the resonancepoint of the resonance circuit. By increasing the impedance at theresonance point as described above, it becomes possible to maintain theamplitude level of the AC voltage that is detected at the time of Qvalue measurement to be high, leading to the improved SN ratio.

It does not matter that the capacitor 32 may be present or may not bepresent (may be a series resonance circuit at the time of electric powersupply).

Furthermore, the capacitor 33′ is connected in series with the capacitor33, and decreases the electrostatic capacitance value in series with thesecondary side coil 31 at the time of electric power supply. Bydecreasing the electrostatic capacitance value in series with thesecondary side coil 31 at the time of Q value measurement, it ispossible to increase the frequency at the resonance point.

As a result, it is possible to restore the resonance frequency that hasbecome low as a result of increasing the electrostatic capacitance valueparallel to the secondary side coil 31 at the time of Q valuemeasurement. In addition, as described above, in the case of a frequencyhaving a low Q value at the frequency at the time of electric powersupply, it is possible to increase the frequency at the time of Q valuemeasurement.

For the Q value measurement circuit of the electric power receivingapparatus 30A, the configuration of the Q value measurement circuit 60shown in FIG. 6 can be used. The Q value measurement circuit 60 measuresthe voltage (voltage V1′) at both ends of capacitors 33 and 33′, whichare connected in series with each other, that is, the voltage (voltageV1′) at the spot or node of V1′ of the resonance circuit and the voltage(voltage V2) at the spot or node of V2.

As described above, by appropriately switching between the thirdswitches 40 to 43, and 43′, it is possible to prevent the measurementsignal (sine wave signal) that is output by the AC power supply of thesecondary side used for the Q value measurement from interfering withthe electric power supply signal supplied from the primary side, and itis possible to calculate a highly accurate Q value.

Moreover, by making the configuration of the resonance circuit at thetime of electric power supply and the configuration of the resonancecircuit at the time of metal foreign matter detection by the Q valuemeasurement to be optimal configurations (constant: electrostaticcapacitance value), it is possible to improve the detection accuracy ofmetal foreign matter without deteriorating electric power supplyperformance.

Furthermore, even when electric power supply is not performed from theelectric power transmission side to the electric power receiving side,the detection of metal foreign matter that exists between the electricpower transmission side and the electric power receiving side isperformed, and the configuration of the resonance circuit is switched atthe time of metal foreign matter detection by the Q value measurement,thereby improving the detection accuracy. Therefore, a frequency that isdifferent from that at the time of electric power supply is selected atthe time of metal foreign matter detection by the Q value measurement,and is supplied to the resonance circuit, so that it is possible todetect metal foreign matter by the Q value measurement without dependingon the diameter of the coil, and the wireless electric power supplymethod (magnitude of coupling coefficient), such as an electromagneticinduction method and a magnetic-field resonance method.

In the example of FIG. 16, a case has been described in which whenshifting from the electric power supply to the Q value measurement, thecircuit configuration of the resonance circuit is switched, and theresonance frequency is increased. As can be understood from FIGS. 1 to3, in a case where the resonance frequency is high, it may be lowered toa frequency at which the Q value becomes a maximum, and the Q valuemeasurement may be performed.

Furthermore, in the example of FIG. 16, a case has been described inwhich when shifting from the electric power supply to the Q valuemeasurement, the value of the capacitance (electrostatic capacitancecomponents) that is in parallel with or in series with the coil of theresonance circuit is changed. However, only the capacitance in parallelwith the coil may be changed (increase for example) or only thecapacitance in series with the coil may be changed (decrease forexample). In order to change the capacitance, the capacitor may beswitched to another capacitor so as to change the capacitance.

In the present embodiment, the connection form of the capacitor for thecoil of the resonance circuit can be applied to any of the following:

(1) Series connection to coil (2) Series connection to coil afterparallel connection (3) Parallel connection to coil

In a case where the capacitor of the resonance circuit not at the timeof Q value measurement is only at the parallel connection to the coil ofthe above (3), when, for example, there is no capacitor 33 with respectto the secondary side coil 31 of FIG. 16, and only the parallelcapacitor 32 is connected, only the capacitor 33′ is connected in serieswith the parallel connection of the secondary side coil 31 and thecapacitor of the resonance circuit when the third switch is turned on.

Entire Control of a Wireless Electric Power Transmission System

Here, a description will be given of the entire control process of thenon-contact electric power transmission system according to the firstembodiment of the disclosure.

FIG. 17 is a flowchart illustrating processing at the time of electricpower supply of a non-contact electric power transmission system, whichis constituted by including the electric power transmission apparatus 10(see FIG. 5) and the electric power receiving apparatus 30A (see FIG.16).

First, when the electric power transmission apparatus 10 (primary side)is started, and the electric power receiving apparatus 30A (secondaryside) is placed near the electric power transmission apparatus 10,negotiation is performed between the electric power transmissionapparatus 10 and the electric power receiving apparatus 30A. After theelectric power transmission apparatus 10 and the electric powerreceiving apparatus 30A recognize each other, electric power supplystarts. The electric power transmission apparatus 10 or the electricpower receiving apparatus 30A performs Q value measurement when startingelectric power supply. Whether or not the count of the Q valuemeasurements is one is determined (step S1).

As an example, in the case of immediately after the power supply of theelectric power transmission apparatus 10 or the electric power receivingapparatus 30A is switched on, each device determines that this is afirst Q value measurement. Alternatively, as a result of thenegotiation, when the electric power transmission apparatus 10recognizes that the electric power receiving apparatus 30A is a firstcommunication party on the basis of the ID (identification) informationof the electric power receiving apparatus 30A, the electric powertransmission apparatus 10 determines that this is a first Q valuemeasurement. Alternatively, at the time of negotiation, the electricpower transmission apparatus 10 may receive the result of the Q valuemeasurement count calculated by the electric power receiving apparatus30A from the electric power receiving apparatus 30A, and know the countof the Q value measurements.

As another example, the Q value measurement count calculated may bedetermined on the basis of the elapsed time period from the previous Qvalue measurement. The electric power transmission apparatus 10 (and theelectric power receiving apparatus 30A) includes a clock unit (notshown). When Q value measurement is performed, the electric powertransmission apparatus 10 (and the electric power receiving apparatus30A) stores the measured Q value in the memory 24 (and the memory 48) insuch a manner as to be associated with the previous measurement time.Then, by comparing the Q value measurement time with the current Q valuemeasurement time, the electric power transmission apparatus 10 (and theelectric power receiving apparatus 30A) determines that this is a firstQ value measurement if there is a time difference exceeding a certainvalue. Q value measurement involving, for example, frequency sweep isdefined a first time measurement, and the count is calculated on thebasis of this. The timer function of the clock unit may be started atthe time of the previous Q value measurement, and the Q valuemeasurement may be determined on the basis of the elapsed time period ofthe timer.

Then, in the case of the first Q value measurement, the electric powerreceiving apparatus 30A uses a plurality of frequencies (sweepmeasurement) for a test signal (sine wave) to be measured, which isoutput by the AC power supply 50, and obtains the highest Q value amongthe plurality of secondary side Q values obtained (step S2). Theelectric power receiving apparatus 30A stores the frequency of the testsignal when the Q value is maximum in the memory 48. The details of theprocess of step S2 will be described later.

In order to measure the Q value, it may be necessary to input the sinewave of the resonance frequency to the electric power receivingapparatus 30A. However, the resonance frequency changes depending onvariations in the quality of parts of the electric power receivingapparatus 30A, variations in the positional relationship between thecoil at the time of mounting and the metal (for example, the housing)inside the apparatus, the environment in the surroundings of thesecondary side coil 31, the mixture of metal foreign matter, and thelike. For this reason, by considering the shift of the resonancefrequency and by performing measurement (frequency sweep) by using aplurality of different frequencies at an appropriate range (measurementrange) to a certain degree, it is necessary to search for the resonancefrequency.

Regarding this frequency sweep, when the entire non-contact electricpower transmission system is considered, the frequency sweep istypically necessary at the first Q value measurement, but can be omittedin the second and subsequent times. An example in which frequency sweepcan be omitted in the second and subsequent Q value measurementsincludes a case in which the positional relationship between theelectric power transmission apparatus 10 and the electric powerreceiving apparatus 30A is not greatly changed from that at the first Qvalue measurement time.

On the other hand, in a case where the Q value measurement is not afirst Q value measurement in the determination process of step S1, theelectric power receiving apparatus 30A obtains the Q value by using atest signal of a frequency obtained at the first Q value measurement(step S3). The details of the process of step S3 will be describedlater.

The electric power transmission apparatus 10 or the electric powerreceiving apparatus 30A determines whether or not metal foreign matteris present on the basis of the secondary side Q value (step S4). Whenthere is no probability that the metal foreign matter is present, theprocess proceeds to step S6.

On the other hand, when there is a probability that the metal foreignmatter is present in the determination process of step S4, the processproceeds to step S2, where the electric power receiving apparatus 30Aperforms the frequency sweep of a test signal, and obtains the highest Qvalue among the plurality of secondary side Q values.

After the process of step S2 is completed, the electric powertransmission apparatus 10 or the electric power receiving apparatus 30Amakes a determination as to the presence or absence of metal foreignmatter on the basis of the secondary side Q value obtained by thecalculation (step S5). When metal foreign matter is present, since theprocessing is completed, the electric power supply is forcedlycompleted, and a warning for the user is given. Examples of electricpower supply forced ending process include a method in which theelectric power transmission apparatus 10 stops electric powertransmission and a method in which even if the electric powertransmission apparatus 10 performs electric power transmission, theelectric power receiving apparatus 30A stops electric power reception.

The above-mentioned Q value measurements in steps S2 to S5 are used byusing the electric power charged into the power storage unit (capacitor35). For example, in the case of frequency sweep, after the capacitor 35has been charged with enough electric charge to measure the Q value(that is, voltage V1′, V2) for the test signal of one frequency, thefollowing is repeated: Q value measurement is performed, charging isperformed once more, and the Q value is measured for the test signal ofthe next frequency.

Then, when there is no metal foreign matter in step S5, electric powersupply is performed for a predetermined time period from the electricpower transmission apparatus 10 to the electric power receivingapparatus 30A (step S6).

Finally, the electric power receiving apparatus 30A determines whetheror not the battery (load) (not shown) or the like is fully charged, andcommunicates the result to the electric power transmission apparatus 10(step S7). When the battery (load) is fully charged, the chargingprocess is completed, and when the battery (load) is not fully charged,the process shifts to step S1, and the above-described processing isrepeated. The determination as to whether or not the battery (load) isfully charged, and the communication may be performed during electricpower supply.

As described above, frequency sweep may be performed at only the first Qvalue measurement, and at second and subsequent times, the Q valuemeasurement may be performed by using only the test signal of thefrequency, which is assumed to be optimum at the first time. However,when a determination is made such that there is a probability that metalforeign matter is present at second and subsequent times, there is aprobability of frequency offset due to that the positional relationshipbetween the primary side coil and the secondary side coil has changed.Thus, the frequency is swept once more so as to make a determination. Inthe case where it is determined that there is metal foreign matter evenif the frequency is swept, the electric power supply is forcedlycompleted and a warning for the user is given. This technique makes itpossible to considerably decrease the time period of the Q valuemeasurement.

Example in which Q Value Calculation Involving Frequency Sweep isPerformed on Primary Side

Next, a description will be given of a case in which a Q valuecalculation involving frequency sweep at step S2 is performed on theprimary side.

Since frequency sweep is performed, it is presupposed that the Q valuecalculation is determined to be a first Q value measurement. For thepresent process, a case is considered in which the electric powertransmission apparatus 10 has determined that the Q value calculation isa first Q value measurement, or a case is considered in which theelectric power receiving apparatus 30A has determined that the Q valuecalculation is a first Q value measurement and has transmitted theresult thereof to the electric power transmission apparatus 10.

FIG. 18 is a flowchart illustrating processing in a case where a Q valuecalculation is to be performed, in which frequency sweep is reflected,on the primary side (electric power transmission apparatus 10).

First, after the negotiation with the main control unit 47 of theelectric power receiving apparatus 30A is completed, the main controlunit 23 of the electric power transmission apparatus 10 causes anelectromagnetic wave to be output from the primary side coil 15 so as tostart the electric power transmission process (transmission of a carriersignal) to the electric power receiving apparatus 30A (step S11). Themain control unit 47 of the electric power receiving apparatus 30Areceives the electromagnetic wave output by the electric powertransmission apparatus 10 from the secondary side coil 31, and starts anelectric power receiving process (step S12).

When an electric power transmission process starts, the main controlunit 23 of the electric power transmission apparatus 10 transmits afirst Q value measurement command to the electric power receivingapparatus 30A through the communication control unit 25 (step S13). Themain control unit 47 of the electric power receiving apparatus 30Areceives the first Q value measurement command from the electric powertransmission apparatus 10 through the communication control unit 49(step S14).

FIG. 19 is an operation timing chart in the non-contact electric powertransmission system according to the first exemplary embodiment of thepresent disclosure.

In the present embodiment, a “Q value measurement period (61-1, 61-2,61-3)” during which a Q value measurement process is performed, and an“electric power supply period (62)” during which a process, such aselectric power supply (other than Q value measurement), are alternatelyset. When the communication between the electric power transmissionapparatus 10 and the electric power receiving apparatus 30A isestablished, the main control unit 23 of the electric power transmissionapparatus 10 issues a first Q value measurement command in step S13above. As an example, the first Q value measurement command istransmitted at the start of the first Q value measurement period 61-1.The first Q value measurement period has been divided into a pluralityof periods of “charging”, “Q value measurement at frequency f.sub.1”,“charging”, “Q value measurement at frequency f.sub.2”, . . . , “Q valuemeasurement at frequency f.sub.n−1”, “charging”, “Q value measurement atfrequency f.sub.n”, “charging”, and “communication to primary side”.

The main control unit 47 of the electric power receiving apparatus 30Aswitches on/off of the first switch 38, the second switch 39, and thethird switches 40 to 43, and 43′ in such a manner as to correspond tothe plurality of periods. The following are main switching timings ofthe first switch 38, the second switch 39, and the third switches 40 to43, and 43′.

1) First switch 38 is turned on in Q value measurement period (capacitor35 is charged) and is turned off in other than that period (electricpower supply period)

2) Second switch 39 is turned off in Q value measurement period and isturned on in other than that period (electric power supply period)

3) Third switches 40 to 43 and 43′ are turned on in the Q valuemeasurement period (in particular, at the time of voltage V1′, V2detection), and are turned off in other than that period

When the main control unit 47 of the electric power receiving apparatus30A receives the first Q value measurement command, the main controlunit 47 turns on the first switch 38 so as to electrically connect therectifying unit 34 and the capacitor 35, and charges the electric powerreceived from the primary side. At this time, the second switch 39 isturned off, and the first regulator 36, that is, the load, isdisconnected from the capacitor 35 (step S15).

Next, the AC power supply 50 of the electric power receiving apparatus30A outputs a test signal (sine wave) for measurement under the controlof the main control unit 47. The frequency Freq of the test signal atthis time is set to an initial value (f.sub.1) (step S16).

The main control unit 23 of the electric power transmission apparatus 10stops the electric power transmission (transmission of a carrier signal)to the electric power receiving apparatus 30A (step S17). The waitingtime period from the electric power transmission start in step S13 untilthe electric power transmission stop in step S17 is the same as or morethan the time period that is necessary for the capacitor 35 to becharged with at least the necessary electric power (electric powernecessary Q value measurement at one frequency).

The main control unit 47 of the electric power receiving apparatus 30Astops electric power reception as a result of the electric powertransmission having been stopped from the electric power transmissionapparatus 10 (step S18).

Here, the main control unit 47 turns on the third switches 40 to 43, and43′ (step S19). As a result of the third switch 40 being turned on, thetest signal of the frequency f.sub.1, which is generated by the AC powersupply 50, is supplied to the other end of the capacitor 33′ through thethird switch 40. Furthermore, as a result of the third switch 41 beingturned on, the other end of the capacitor 33′ is made to conduct withthe input end of the amplifier 44A, and as a result of the third switch42 being turned on, one end of the capacitor 33 is made to conduct withthe input end of the amplifier 44B.

Then, the main control unit 47 causes the amplifier 44A, the envelopedetection unit 45A, and the ADC 46A to detect the voltage V1′ at theother end of the capacitor 33′, and records the voltage V1′ in thememory 48. Similarly, the main control unit 47 causes the amplifier 44B,the envelope detection unit 45B, and the ADC 46B to detect the voltageV2 at one end of the capacitor 33, and records the voltage V2 in thememory 48 (step S20).

After the voltages V1′ and V2 when the frequency of the test signal isf.sub.1 are obtained, the main control unit 47 turns off the thirdswitches 40 to 43, and 43′ (step S21).

Here, the main control unit 23 of the electric power transmissionapparatus 10 starts again the electric power transmission to theelectric power receiving apparatus 30A (step S22). The waiting timeperiod from the electric power transmission stop in step S17 until theelectric power transmission start in step S22 is the same as or morethan the time period necessary to at least detect and record thevoltages V1′ and V2. Then, after the main control unit 23 of theelectric power transmission apparatus 10 restarts the electric powertransmission to the electric power receiving apparatus 30A in step S22,the process proceeds to step S17 after the waiting time period for thecharging in the capacitor 35 has passed, and the main control unit 23stops the electric power transmission again. The waiting time periodfrom the electric power transmission start in step S22 until theelectric power transmission stop in step S17 is the same as or more thanthe time period necessary for the capacitor 35 to be charged with atleast necessary electric power.

In response to the restart of the electric power transmission of theelectric power transmission apparatus 10, the main control unit 47 ofthe electric power receiving apparatus 30A starts the electric powerreception from the electric power transmission apparatus 10 and chargesthe capacitor 35 (step S23). During the waiting time period of thecharging of the capacitor 35, the AC power supply 50 of the electricpower receiving apparatus 30A outputs the test signal of the nextfrequency Freq under the control of the main control unit 47 (step S24).The frequency Freq of the test signal at this time is set to f.sub.2.

After the process of step S24 is completed, the main control unit 47 ofthe electric power receiving apparatus 30A proceeds to step S18 afterthe waiting time period of the charging of the capacitor 35 has passed,and the main control unit 47 stops electric power reception due to thatelectric power transmission is stopped from the electric powertransmission apparatus 10. Then, the main control unit 47 continuesprocessing subsequent to step S19, and performs Q value measurementsusing the test signal of the frequency f.sub.2 so as to obtain thevoltages V1′ and V2.

During the time period from the electric power reception stop in stepS18 until the electric power reception start in step S23 (steps S19 toS21), blocks of the detection circuit operate with only the electricpower that has been charged in the capacitor 35.

When a process (frequency sweep) for obtaining the voltages V1′ and V2for each test signal of a plurality of frequencies is completed, themain control unit 47 of the electric power receiving apparatus 30A turnsoff the first switch 38 so as to disconnect the capacitor 35 from thedetection circuit (step S25). Next, the main control unit 47 of theelectric power receiving apparatus 30A controls the AC power supply 50so as to stop the output of the test signal (step S26).

Then, the main control unit 47 of the electric power receiving apparatus30A responds with the first Q value measurement command from theelectric power transmission apparatus 10. As a response, a measured datagroup (Freq, V1, V2) obtained by using the threshold value used for thedetermination as to the presence or absence of metal foreign matter,which is stored in the memory 48, and test signals of a plurality offrequencies, are sent back to the electric power transmission apparatus10 through the communication control unit 49 (step S27).

In the flowchart shown in FIG. 18, while the capacitor 35 is beingcharged, the second switch 39 is turned off, and the first regulator 36(load) is disconnected from the capacitor 35 (see step S15).Alternatively, electric power may be supplied to the load while thecapacitor 35 is being charged. Stopping the electric power supply(charging of the capacitor 35) may be at least at the time of Q valuemeasurement (in particular, at the time of the detection of voltages V1′and V2). While communication is being performed and charging is beingperformed in the capacitor 35, electric power supply may be eithercontinued or stopped. This also applies in the flowchart of FIG. 21 (tobe described later).

After the process of step S27, the electric power transmission apparatus10 receives the threshold value and the measured data group (Freq, V1′,V2) from the electric power receiving apparatus 30A, and stores them inthe memory 24 (step S28).

Then, on the basis of Equation (1), the computation processing unit 23Aof the electric power transmission apparatus 10 calculates the Q valueof the secondary side on the basis of the voltages V1′ and V2 for eachfrequency Freq of the test signal received from the electric powerreceiving apparatus 30A, generates a table of frequencies and Q values,and stores the table in the memory 24. The relationship between thefrequencies and the Q values of the test signal is expressed as a graphin FIG. 20. The highest Q value (Q_Max) on the secondary side isdetermined (step S29). In the example of FIG. 11, the Q value at thefrequency f.sub.0 in the vicinity of the local maximum value of thefrequency characteristic curve of the Q value becomes Q_Max.

Next, the determination unit 23B of the electric power transmissionapparatus 10 compares Q_Max with the threshold value stored in thememory 24 so as to determine whether or not Q_Max is lower than thethreshold value (step S30).

When Q_Max is lower than the threshold value in the determinationprocess of step S30, the determination unit 23B determines that there ismetal foreign matter (step S5 in FIG. 17), and performs an endingprocess. On the other hand, if Q_Max is not lower than the thresholdvalue, the determination unit 23B determines that there is no metalforeign matter (step S5 in FIG. 17), and the process proceeds to stepS6.

For example, in a case where a measurement result has been obtained suchthat there is an amount of change in a Q value of at least 25% betweenwhen there is no metal foreign matter and when there is metal foreignmatter is obtained, as an example, a value such that 25% is subtractedfrom the Q value when there is foreign matter metal may be set as athreshold value. Regarding this threshold value, since the amount ofchange in the Q value changes with on the configuration of the electricpower receiving apparatus, the environment, the size and the type of themetal foreign matter to be detected, and the like, it is preferable thatthe threshold value be set as appropriate in accordance with themeasurement target.

Example in which Q Value Calculations of Second and Subsequent Times isPerformed on Primary Side

Next, a description will be given of processing in a case where Q valuecalculations (process in step S3) of second and subsequent times areperformed on the primary side. In this example, a case in which a secondQ value measurement after frequency sweep is performed is performed willbe described. The same also applies to Q value measurements at third andsubsequent times.

FIG. 21 is a flowchart illustrating processing in a case where a Q valuecalculation is performed on the primary side (electric powertransmission apparatus).

The processing of steps S41 to S55 of FIG. 21 corresponds to theprocessing of steps S11 to S26 (excluding step S24) of FIG. 18. In thefollowing, differences between FIG. 18 and FIG. 21 will be mainlydescribed.

When the electric power transmission process starts in steps S41 andS42, the main control unit 23 of the electric power transmissionapparatus 10 transmits the second Q value measurement command to theelectric power receiving apparatus 30A through the communication controlunit 25 (step S43). The main control unit 47 of the electric powerreceiving apparatus 30A receives the second Q value measurement commandfrom the electric power transmission apparatus 10 through thecommunication control unit 49 (step S44).

As an example, the second Q value measurement command is transmitted atthe start of the second Q value measurement period (see FIG. 19). Thesecond Q value measurement period is divided into four periods, namely,“charging”, “Q value measurement at frequency f.sub.0”, “charging”, and“communication with primary side”. The main control unit 47 of theelectric power receiving apparatus 30A switches on/off of the firstswitch 38, the second switch 39, and the third switches 40 to 43 and 43in such a manner as to correspond to these four periods.

When the main control unit 47 of the electric power receiving apparatus30A receives the second Q value measurement command, the main controlunit 47 turns on the first switch 38, so that the capacitor 35 isconnected to the detection circuit and is charged. At this time, themain control unit 47 turns off the second switch 39, so that the firstregulator 36, that is, the load, is disconnected from the capacitor 35(step S45).

Next, the AC power supply 50 of the electric power receiving apparatus30A outputs a test signal (sine wave) for measurement under the controlof the main control unit 47. The frequency Freq of the test signal atthis time is set to a frequency f.sub.0 (.apprxeq.resonance frequency)when the highest Q value (Q_Max) was obtained in the previous frequencysweep process (step S46).

The main control unit 23 of the electric power transmission apparatus 10stops the electric power transmission (transmission of a carrier signal)to the electric power receiving apparatus 30A (step S47). The waitingtime period from the electric power transmission start in step S43 untilthe electric power transmission stop in step S47 is the same as or morethan the time period necessary for the capacitor 35 to be charged withat least necessary electric power (electric power necessary for Q valuemeasurement at one frequency).

The main control unit 47 of the electric power receiving apparatus 30Astops the electric power reception because the electric powertransmission has been stopped from the electric power transmissionapparatus 10 (step S48).

Here, the main control unit 47 turns on the third switches 40 to 43(step S49). Then, the main control unit 47 detects the voltage V1′ atthe other end of the capacitor 33′, records the voltage V1′ in thememory 48, and similarly, detects the voltage V2 at one end of thecapacitor 33, and records the voltage V2 in the memory 48 (step S50).After the voltages V1′ and V2 when the frequency of the test signal isf.sub.0 are obtained, the main control unit 47 turns off the thirdswitches 40 to 43, and 43′ (step S51).

Here, the main control unit 23 of the electric power transmissionapparatus 10 starts the electric power transmission to the electricpower receiving apparatus 30A again (step S52). The waiting time periodfrom the electric power transmission stop in step S47 until the electricpower transmission start in step S52 is the same as or more than thetime period necessary for the voltages V1′ and V2 to be at leastdetected and recorded. In FIG. 18, after the electric power transmissionto the electric power receiving apparatus 30A restarts, the electricpower transmission is stopped again after the waiting time period of thecharging of the capacitor 35 has passed. However, in this example, theelectric power transmission stop for the second time is not performedbecause it is sufficient that measured data when the frequency of thetest signal is f.sub.0 can be obtained.

In response to the restart of the electric power transmission of theelectric power transmission apparatus 10, the main control unit 47 ofthe electric power receiving apparatus 30A starts the electric powerreception from the electric power transmission apparatus 10, and chargesthe capacitor 35 (step S53).

In FIGS. 9A, 9B, and 9C, in the waiting time period of the charging ofthe capacitor 35, the output (see step S24) of the test signal at thenext frequency Freq (f.sub.2) is performed; however, in this example,the output of the test signal is not performed.

In the case where the process for obtaining the voltages V1′ and V2 whenthe frequency of the test signal is f.sub.0 is completed, the maincontrol unit 47 of the electric power receiving apparatus 30A turns offthe first switch 38 so as to disconnect the capacitor 35 from thedetection circuit (step S54). Next, the main control unit 47 of theelectric power receiving apparatus 30A controls the AC power supply 50so as to stop the output of the test signal (step S55).

Then, the main control unit 47 of the electric power receiving apparatus30A responds with the second Q value measurement command from theelectric power transmission apparatus 10. As a response, the maincontrol unit 47 sends back the threshold value used for thedetermination as to the presence or absence of metal foreign matter,which has been stored in the memory 48, and the measured data group(f.sub.0, V1′, V2) when the frequency of the test signal is f.sub.0, tothe electric power transmission apparatus 10 through the communicationcontrol unit 49 (step S56).

The electric power transmission apparatus 10 receives the thresholdvalue and the measured data group (f.sub.0, V1′, V2) from the electricpower receiving apparatus 30A, and stores them in the memory 24 (stepS57).

Then, in accordance with Equation (1), the computation processing unit23A of the electric power transmission apparatus 10 calculates the Qvalue on the secondary side on the basis of the voltages V1′ and V2,which have been obtained in the case of the test signal of the frequencyf.sub.0 received from the electric power receiving apparatus 30A (stepS58).

Next, the determination unit 23B of the electric power transmissionapparatus 10 compares the calculated Q value on the secondary side withthe Q_Max at the time of frequency sweep, which has been stored in thememory 24, so as to determine whether or not the Q value falls within apredetermined range of Q_Max. As a specific example, it is determinedwhether or not the Q value is lower than Q_Max by X % (step S59). Thatis, Q_Max at the previous frequency sweep is used as a standard Q valueso as to detect metal foreign matter.

In the determination process of step S59, when the Q value is lower thanQ_Max by X % or more, the determination unit 23B determines that metalforeign matter is possibly present (step S4 in FIG. 17), and the processproceeds to step S2. On the other hand, when the Q value is not lowerthan Q_Max by X %, the determination unit 23B determines that metalforeign matter is not present (step S4 in FIG. 17), and the processproceeds to step S6.

In the determination process, the reason when the Q value is lower thanQ_Max by X % or more, it is determined that the metal foreign matter maybe “present” is that, as has already been described, a frequency offsetmay have occurred due to that the positional relationship between theprimary side coil and the secondary side coil has changed. That is, atthe time of the second Q value measurement, the frequency may be shiftedfrom the resonance frequency f.sub.0 obtained at the first Q valuemeasurement (frequency sweep). Therefore, there is a probability thatthe value of the Q value markedly differs between the Q value (Q_Max) inthe case of the resonance frequency f.sub.0 obtained by the first Qvalue measurement (frequency sweep) and the second Q value measurementusing the resonance frequency f.sub.0.

Hence, when the Q value is lower than Q_Max by X % or more in the secondQ value measurement, it is determined that metal foreign matter ispossibly present, and the process proceeds to step S2, where thefrequency sweep process is performed once more, so that a more certaindetermination as to the presence or absence of metal foreign matter isperformed.

Modification

Example in which Q Value Calculation is Performed on Secondary Side

In the examples of FIGS. 18 and 21, the threshold value used for thedetermination as to the presence or absence of metal foreign matter andthe measured data group (f.sub.0, V1′, V2) when the frequency of thetest signal is f.sub.0 are transmitted from the electric power receivingapparatus 30A (secondary side) to the electric power transmissionapparatus (primary side) 10. Then, in the electric power transmissionapparatus 10, the Q value is calculated on the basis of the voltages V1′and V2 of the measured data group, and the Q value is compared with thethreshold value so as to determine the presence or absence of metalforeign matter.

However, the electric power receiving apparatus 30A may measure the Qvalue on the basis of the measured data group (f.sub.0, V1′, V2) whenthe frequency of the test signal is f.sub.0, and may compare the Q valuewith the threshold value so as to determine the presence or absence ofmetal foreign matter. That is, only the determination result of thepresence or absence of metal foreign matter is transmitted to theelectric power transmission apparatus 10 from the electric powerreceiving apparatus 30A.

As shown in FIG. 18, when the electric power transmission apparatus 10(primary side) calculates the Q value and determines the presence orabsence of metal foreign matter, there is advantage that the electricpower receiving apparatus 30A (secondary side) is not necessary to havehardware of a computation processing unit and a determination unit. Forexample, a reduction in size, a lighter weight, and cost reduction of aportable device used as the electric power receiving apparatus 30A canbe expected.

On the other hand, when the electric power receiving apparatus 30Acalculates a Q value and determines the presence or absence of metalforeign matter, it is necessary for the electric power receivingapparatus 30A to have hardware of a computation processing unit and adetermination unit. However, since the information on the determinationresult such that metal foreign matter is present or metal foreign matteris not present is only sent to the electric power transmission apparatus10, the amount of information is small and the reduction in thecommunication time period can be expected.

2. Second Embodiment

FIG. 22 is a block diagram illustrating the main portion of an exampleof the internal configuration of an electric power transmissionapparatus (primary side) that switches the configuration (constant) of aresonance circuit between electric power supply time and Q valuemeasurement time according to a second exemplary embodiment of thepresent disclosure.

In the electric power transmission apparatus 10A according to thepresent embodiment, the same configuration as that of the resonancecircuit of the electric power receiving apparatus 30A (see FIG. 6) isapplied to the electric power transmission apparatus 10 shown in FIG. 5.That is, capacitors 72, 72′, 73, and 73′ forming the resonance circuitof the electric power transmission apparatus 10A correspond to thecapacitors 32, 32′, 33, and 33′ forming the resonance circuit of theelectric power receiving apparatus 30A.

The third switches 40 to 43, and 43′ used for the electric powerreceiving apparatus 30A are connected to this resonance circuit, andalso the third switches 40 to 42 are connected to the Q valuemeasurement circuit 20′.

In contrast with the Q value measurement circuit 20, the Q valuemeasurement circuit 20′ includes the AC power supply (oscillationcircuit), the resistance element, and the amplifier shown in FIG. 6(illustrations of all of which are omitted), and supplies analternating-current signal (sine wave) to one end of the capacitor 73through the third switch 40. The third switches 41 and 42 are connectedto the rectifying units 21A and 21B of the Q value measurement circuit20′, respectively.

The Q value measurement circuit 20′ (main control unit 23) controlson/off of the third switches 40 to 43 and 43′ so as to switch theconfiguration of the resonance circuit between electric power supplytime and Q value measurement time, and the Q value measurement circuit20′ measures the voltage V1′ and the voltage V2 at the time of electricpower supply.

The signal source 11 includes an electric power transmission apparatusunit 21 for outputting a control signal used to control the generationof an alternating-current signal, and an electric power transmissiondriver 22 for generating and outputting an alternating-current signal ofa given frequency on the basis of the control signal of the electricpower transmission apparatus unit 21. The electric power transmissionapparatus unit 21 and the electric power transmission driver 22 outputan alternating-current signal to the outside through the primary sidecoil 71 of the resonance circuit at a time that is not at least the Qvalue measurement time.

When the third switch and the Q detection measurement circuit, which areprovided in the electric power transmission apparatus, are to beoperated, for the power supply therefor, an alternating-current signalthat is output by the signal source 11 or the stored electric power of abattery (not shown) included in the electric power transmissionapparatus, or the like can be used.

FIG. 23 is an equivalent circuit diagram illustrating the configurationof a resonance circuit when the third switch of the electric powertransmission apparatus 10A is turned on and off.

In the present exemplary embodiment, the third switch is turned off atelectric power supply time, and the primary side coil 71, and thecapacitors 72 and 73 constitute a resonance circuit (the upper side inFIG. 23).

On the other hand, the third switch is turned on at Q value measurementtime, a capacitor 72′ is further connected in parallel to the capacitor72 in parallel with the primary side coil 71, and a capacitor 73′ isfurther connected to the capacitor 73 in series with the primary sidecoil 71 (the lower side in FIG. 23).

By assuming that the above-mentioned 8-turns coil is used for theprimary side coil 71, the constants of the resonance circuit werecalculated when the third switches 40 to 43 and 43′ were on and off.

When the third switches 40 to 43 and 43′ were off, the results wereobtained in which the resonance frequency of the resonance circuit was121.6 kHz, the impedance of the resonance circuit at the resonance pointwas 0.7.OMEGA., and the Q value was 50. The conditions used for trialcalculations are: the amplitude of the AC voltage is 0.1V, theself-inductance of the primary side coil 71 of the resonance circuit is14.3.mu.H, the resistance value of the effective resistance component r1is 0.6.OMEGA., and the electrostatic capacitance values of thecapacitors 72 and 73 are 10 nF and 110 nF, respectively.

On the other hand, when the third switches 40 to 43 and 43′ were on, theresults were obtained in which the resonance frequency of the resonancecircuit was 227.5 kHz, the impedance of the resonance circuit at theresonance point was 8.3.OMEGA., and the Q value was 82.

The electrostatic capacitance values of the capacitors 72′ and 73′ were15 nF and 10 nF, respectively, and the other conditions were the same asthose described above.

In the present embodiment, similarly to the first embodiment, byappropriately switching the third switches 40 to 43 and 43′, it ispossible to prevent the measurement signal (sine wave signal) that isoutput by the AC power supply of the secondary side, which is used forthe Q value measurement, from interfering with the electric power supplysignal supplied from the primary side, and it is possible to calculate ahighly accurate Q value.

Moreover, by making the configuration of the resonance circuit at thetime of electric power supply and the configuration of the resonancecircuit at the time of metal foreign matter detection by using Q valuemeasurement to be optimal configurations (constant: electrostaticcapacitance value), it is possible to improve the detection accuracy ofmetal foreign matter without deteriorating electric power supplyperformance.

Furthermore, similarly to the first embodiment, not limited to themagnetic-field resonance method, the second embodiment can also beapplied to an electromagnetic induction method in which a couplingcoefficient k is high and the Q value is minimized.

Also, in the present embodiment, the second embodiment can be applied toall of the cases in which the connection form of the capacitor to thecoil of the resonance circuit is (1) series connection to the coil; (2)series connection to the coil after parallel connection; and (3)parallel connection to the coil.

In the examples of FIGS. 16, 22, and 23, by switching the circuitconfiguration of the resonance circuit, the resonance frequency of theresonance circuit is increased, and the impedance is also increased. Incontrast, as shown in FIGS. 9A, 9B, and 9C to 12, only the impedance ofthe resonance circuit may be changed without changing the resonancefrequency of the resonance circuit.

In addition, in the examples of FIGS. 16, 22, and 23, a case has beendescribed in which the capacitance of the capacitor forming theresonance circuit is changed. Alternatively, the self-inductance of thecoil forming the resonance circuit may be changed.

In that case, for example, by using a tapped coil for a coil, byswitching the tap or selecting a tap between the electric power supplytime and Q value measurement time by the circuit switching unit underthe control of the main control unit 23, and by thereby changing thecoil that substantially forms the resonance circuit, the self-inductanceof the coil of the resonance circuit is changed. Alternatively, the coilitself may be switched to another coil.

3. Others First Example

In the above-described first and second exemplary embodiments, the Qvalue measurement circuit 60 (computation processing unit 47A) and the Qvalue measurement circuit 20′ (computation processing unit 23A) obtain aQ value on the basis of the voltage V1′ between the coil of thecapacitor of the resonance circuit and the voltage V2 across the coil.In the present exemplary embodiment, the Q value is obtained inaccordance with a half-power band width method.

In the half-power band width method, in a case where a series resonancecircuit is configured, the Q value is obtained by Equation (9) below onthe basis of the band (frequencies f1 to f2), which is at impedance 2times the absolute value of the impedance (Zpeak) at the resonancefrequency f0, as shown in the graph of FIG. 24.

Q=f0f2−f1(9)  ##EQU00006##

Furthermore, in a case where a parallel resonance circuit is configured,as shown in the graph of FIG. 25, the Q value is obtained by Equation(9) on the basis of the band (frequencies f1 to f2), which is atimpedance ½ times the absolute value of the impedance (Zpeak) at theresonance frequency f0.

Second Example

Unlike the first and second exemplary embodiments, the present exemplaryembodiment is an example in which the computation processing units 47Aand 23A calculate a Q value on the basis of the ratio of the real partcomponents of the impedance of the resonance circuit to the imaginarypart components. In this example, the real part components and theimaginary part components of the impedance are obtained by using anautomatic balanced bridge circuit and a vector ratio detection unit.

FIG. 26 is a circuit diagram of an automatic balanced bridge circuit forcalculating a Q value on the basis of the ratio of the real partcomponents of the impedance to the imaginary part components thereof

An automatic balanced bridge circuit 90 shown in FIG. 26 is configuredthe same as a generally used inverting amplification circuit. A coil 92is connected to the inverting input terminal (−) of an invertingamplifier 93, and a non-inverting input terminal (+) thereof isconnected to the ground. Then, a feedback resistance element 94 appliesnegative feedback to the inverting input terminal (−) from the outputterminal of the inverting amplifier 93. Furthermore, the automaticbalanced bridge circuit 90 inputs the output (voltage V1′) of the ACpower supply 91 that inputs an alternating-current signal to the coil92, and the output (voltage V2) of the inverting amplifier 93 to avector ratio detection unit 95. The coil 92 corresponds to the secondaryside coil 31 of FIG. 16 or the primary side coil 71 of FIG. 22.

The automatic balanced bridge circuit 90 operates in such a manner thatthe voltage of the inverting input terminal (−) is typically zero due tothe action of negative feedback. Furthermore, almost all the electriccurrent that flows through the AC power supply 91 to the coil 92 flowsto the feedback resistance element 94 because the input impedance of theinverting amplifier 93 is large. As a result, the voltage applied to thecoil 92 becomes the same as the voltage V1′ of the AC power supply 91and also, the output voltage of the inverting amplifier 93 becomes theproduct of the electric current I flowing through the coil 92 and thefeedback resistance value Rs. The feedback resistance value Rs is acommonly used reference resistance value. Therefore, when the voltageV1′ and the voltage V2 are detected and the ratio thereof is calculated,the impedance is obtained. In order to obtain the voltage V1′ and thevoltage V2 as complex numbers, the vector ratio detection unit 95 usesthe phase information (short dashed line) of the AC power supply 91.

In this example, by using such an automatic balanced bridge circuit 90,the vector ratio detection unit 95, and the like, the real partcomponents R.sub.L and the imaginary part components X.sub.L of theimpedance Z.sub.L of the resonance circuit are obtained, and a Q valueis obtained on the basis of the ratio thereof. Equation (10) andEquation (11) below are calculation equations showing the processes ofobtaining the Q value.

ZL=RL+jXL=V1I=V1V2Rs(10)Q=XLRL(11)  ##EQU00007##

In the first and second exemplary embodiments, a description has beengiven by assuming the non-contact electric power transmission system ofa magnetic-field resonance method. However, as has already beendescribed, the present disclosure is not limited to the magnetic-fieldresonance method, and can also be applied to an electromagneticinduction method in which the coupling coefficient k is high and the Qvalue is minimized.

Furthermore, the electric power receiving apparatus may include anelectric power transmission unit and may transmit electric power to theelectric power transmission apparatus through a secondary side coil in anon-contact manner. Alternatively, the electric power transmissionapparatus may include a load, and may receive electric power from theelectric power receiving apparatus through an electric powertransmission coil in a non-contact manner.

Furthermore, in the first embodiment, an example has been described inwhich Q value measurement is performed by using small electric powerthat is charged in the capacitor 35 of the electric power receivingapparatus 30A. Alternatively, since it is sufficient that theconfiguration of the resonance circuit is switched between electricpower supply time and Q value measurement time, Q value measurement maybe performed by using the electric power of the battery. In this case,the capacitor 35 is unnecessary.

Furthermore, in the first and second exemplary embodiments, the Q valueat the resonance frequency is measured. However, the frequency at whichthe Q value is measured may not necessarily match the resonancefrequency. Even in the case where the Q value is measured by using afrequency offset from the resonance frequency to a permissible range,use of the technology of the present disclosure makes it possible toimprove the accuracy of detection of metal foreign matter that ispresent between the electric power transmission side and the electricpower receiving side.

Furthermore, as a conductor, such as a metal, approaches a primary sidecoil or a secondary side coil, not only the Q value, but also the Lvalue changes, and the resonance frequency is offset. By using togetherthe amount of offset of the resonance frequency due to a change in the Lvalue, and the Q value, an electromagnetically coupled state may bedetected.

Furthermore, when metal foreign matter is sandwiched between a primaryside coil and a secondary side coil, the coupling coefficient k valuealso changes. In order to detect an electromagnetically coupled state,the changes in the coupling coefficient k value and the Q value may beused together.

Furthermore, in the first and second exemplary embodiments of thepresent disclosure, a description has been given of a coil not having acore as a primary side coil and a secondary side coil. Alternatively, acoil that is constructed to be wound around a core having a magneticsubstance may be adopted.

In addition, in the first and second exemplary embodiments of thepresent disclosure, an example has been described in which a mobilephone is applied to a portable device on the secondary side. Not limitedto this example, the mobile phone can be applied to various portabledevices for which electric power is necessary, such as a portable musicplayer or a digital still camera.

The present disclosure can take the following configurations.

[1] An energy receiver to receive energy in a wireless manner from anenergy transmitter, said energy receiver comprising: a resonance circuitincluding at least an inductor, a first capacitor, and a secondcapacitor; and a Q-value circuit connected to the resonance circuit, theQ-value circuit being configured to obtain a first voltage taken at afirst node of the resonance circuit and a second voltage taken at asecond node of the resonance circuit, wherein, the first and secondcapacitors are connected in series between the first and second nodes.

[2] The energy receiver of [1] above, wherein the Q-value circuitincludes: a computing section to compute a Q-value based on the firstand second voltages, the Q-value being a ratio of the first voltagerelative to the second voltage; and a control section to compare theQ-value with a threshold value to determine if foreign matter is in aspace affecting the wireless reception of energy.

[3] The energy receiver of [1] above, further comprising: a switchingsection having a plurality switches to selectively connect the resonancecircuit to the Q-value circuit, wherein, the Q-value circuit includes acontrol section that is configured to control the switching section suchthat electric power is received by the energy receiver at a differenttime than when the first and second voltages are obtained, and theQ-value circuit is configured to detect an electromagnetically coupledstate of at least the inductor.

[4] The energy receiver of [3] above, wherein: the switching section isoperable to switch to a state in which an electrostatic capacitancevalue of the resonance circuit is decreased.

[5] The energy receiver of [3] above, wherein: the energy receiver isconfigured to switch from a first resonance frequency to a secondresonance frequency, and increase impedance of the resonance circuit.

[6] The energy receiver of [3] above, wherein: the inductor is a tappedcoil, and the switching section is configured to select a tap of thetapped coil.

[7] The energy receiver of [3] above, further comprising: third andfourth capacitors, wherein, the third capacitor is coupled to theinductor, the fourth capacitor is coupled between first ends of each ofthe inductor and the third capacitor and a ground potential.

[8] The energy receiver of [7] above, wherein: the plurality of switchesof the switching section include a first switch and a second switch, thefirst switch is coupled to the third capacitor and a ground potential,and the second switch is coupled between the fourth switch and theground potential.

[9] The energy receiver of [7] above, wherein: the switching section isoperable to switch to a state in which an electrostatic capacitancevalue of the resonance circuit is increased.

[10] A method to detect foreign matter in a space affecting wirelesstransmission of electric power from a transmitter to a receiver, saidmethod comprising: receiving electric energy from a resonance circuitthat includes at least an inductor, a first capacitor, and a secondcapacitor; and obtaining a first voltage taken at a first node of theresonance circuit and a second voltage taken at a second node of theresonance circuit, wherein, the first and second capacitors areconnected in series between the first and second nodes.

[11] The method of [10] above, further comprising: comparing a ratio ofthe first and second voltages with a threshold value to determine ifforeign matter is present in a space affecting wireless powertransmission.

[12] The method of [11] above, further comprising: controlling awireless transmission of electric power based on a result of saidcomparison of the ratio to the threshold value.

[13] An energy transmitter to transmit energy in a wireless manner to anenergy receiver, said energy transmitter comprising: a resonance circuitincluding at least an inductor, a first capacitor, and a secondcapacitor; and a Q-value circuit connected to the resonance circuit, theQ-value circuit being configured to determine a relationship of a firstvoltage taken at a first node relative to a second voltage taken at asecond node, wherein, the first and second capacitors are connected inseries between the first and second nodes.

[14] The energy transmitter according to [13] above, wherein the Q-valuecircuit includes a control section that is configured to compare therelationship of the first voltage and the second voltage with athreshold value to determine if foreign matter is affecting reception ofthe wireless energy transmission.

[15] The energy transmitter according to [13] above, further comprising:a switching section having a plurality switches to selectively connectthe resonance circuit to the Q-value circuit, wherein, the Q-valuecircuit includes a control section that is configured to control theswitching section such that energy transmission occurs at a differenttime than when the first and second voltages are obtained.

[16] The energy transmitter according to [13] above, further comprising:third and fourth capacitors coupled to the inductor, wherein, theswitching section includes first and second switches, the first switchis disposed between the third capacitor and a ground potential, and thesecond switch is disposed between the fourth capacitor and a groundpotential.

[17] A detection device to detect foreign matter in a space affectingwireless electric power transmission, said detection device comprising:a circuit to determine a relationship of a first voltage taken at afirst node relative to a second voltage taken at a second node, wherein,the circuit is connected to a resonance circuit that includes at leastan inductor, a first capacitor, and a second capacitor, and the firstand second capacitors are connected in series between the first andsecond nodes.

[18] A wireless electric power transmission system comprising: atransmitter to transmit electric energy; and a receiver to receive theelectric energy transmitted by the transmitter, wherein one of thetransmitter and the receiver includes: a resonance circuit including atleast an inductor, a first capacitor, and a second capacitor, and aQ-value circuit connected to the resonance circuit, the Q-value circuitbeing configured to determine a relationship of a first voltage taken ata first node relative to a second voltage taken at a second node,wherein, the first and second capacitors are connected in series betweenthe first and second nodes.

[19] A method for wireless power transmission between a transmitter anda receiver, said method comprising: receiving, via a resonance circuit,electric power wirelessly from the transmitter; obtaining, via a Q-valuecircuit, first and second voltages at respective first and second nodesof the resonance circuit, the first and second voltages being effectiveto determine if foreign matter is present in a space affecting wirelesspower transmission; and controlling a switching section between theQ-value circuit and the resonance circuit such that the electric powertransmission occurs at a different time than when the first and secondvoltages are obtained.

[20] The method of [19] above, wherein: the resonance circuit includesan inductor and a first capacitor, and the first and second nodes arepositioned across at least the first capacitor.

[21] A detection apparatus comprising: a resonance circuit including atleast a coil and a capacitor; a detection unit configured to measure a Qvalue of the resonance circuit; a circuit switching unit configured toswitch a circuit configuration of the resonance circuit between electricpower supply time and Q value measurement time; and a control unitconfigured to control switching by the circuit switching unit.

[22] The detection apparatus according to [21] above, wherein thedetection unit measures the Q value of the resonance circuit and detectsan electromagnetically coupled state of the coil and the outside.

[23] The detection apparatus according to [22] above, wherein thecircuit switching unit switches the circuit configuration of theresonance circuit between electric power supply time and Q valuemeasurement time, and changes a resonance frequency of the resonancecircuit.

[24] The detection apparatus according to [22] above, wherein thecircuit switching unit switches the circuit configuration of theresonance circuit between electric power supply time and Q valuemeasurement time, changes the resonance frequency of the resonancecircuit, and increases impedance at the resonance frequency of theresonance circuit.

[25] The detection apparatus according to [22] above, wherein thecircuit switching unit switches the circuit configuration of theresonance circuit between electric power supply time and Q valuemeasurement time, and increases impedance at the resonance frequency ofthe resonance circuit.

[26] The detection apparatus according to [23] above, wherein thecircuit switching unit changes an electrostatic capacitance value ofelectrostatic capacitance components of the resonance circuit at thetime of Q value measurement.

[27] The detection apparatus according to [26] above, wherein thecircuit switching unit changes the electrostatic capacitance value ofthe electrostatic capacitance components in parallel with and in serieswith the coil of the resonance circuit at the time of Q valuemeasurement.

[28] The detection apparatus according to [26] above, wherein thecircuit switching unit changes the electrostatic capacitance value ofthe electrostatic capacitance components in parallel with the coil ofthe resonance circuit at the time of Q value measurement.

[29] The detection apparatus according to [26] above, wherein thecircuit switching unit changes the electrostatic capacitance value ofthe electrostatic capacitance components in series with the coil of theresonance circuit at the time of Q value measurement.

[30] The detection apparatus according to [27] above, wherein thecircuit switching unit increases the electrostatic capacitance value ofthe electrostatic capacitance components in parallel with the coil atthe time of Q value measurement.

[31] The detection apparatus according to [27] above, wherein thecircuit switching unit decreases the electrostatic capacitance value ofthe electrostatic capacitance components in series with the coil at thetime of Q value measurement.

[32] The detection apparatus detection apparatus according to [26]above, wherein the circuit switching unit switches a self-inductance ofthe coil of the resonance circuit at the time of Q value measurement.

[33] The detection apparatus according to [32] above, wherein: the coilis a tapped coil, and the circuit switching unit selects a tap of thetapped coil.

[34] The detection apparatus according to [26] above, wherein theresonance circuit is configured in such a manner that the capacitor isconnected in series with the coil.

[35] The detection apparatus according to [26] above, wherein theresonance circuit is configured in such a manner that the capacitor isconnected in parallel with the coil.

[36] The detection apparatus according to [26] above, wherein theresonance circuit is configured in such a manner that the capacitor isconnected in parallel with the coil and another capacitor is connectedin series with the coil.

[37] An electric power receiving apparatus comprising: a coil configuredto receive electric power; a resonance circuit including at least thecoil and a capacitor; a detection unit configured to measure a Q valueof the resonance circuit; a circuit switching unit configured to switcha circuit configuration of the resonance circuit between electric powersupply time and Q value measurement time; and a control unit configuredto control switching by the circuit switching unit.

[38] An electric power transmission apparatus comprising: a coilconfigured to transmit electric power; a resonance circuit including atleast the coil and a capacitor; a detection unit configured to measure aQ value of the resonance circuit; a circuit switching unit configured toswitch a circuit configuration of the resonance circuit between electricpower supply time and Q value measurement time; and a control unitconfigured to control switching by the circuit switching unit.

[39] A non-contact electric power transmission system comprising: anelectric power transmission apparatus configured to transmit electricpower in a wireless manner; and an electric power receiving apparatusconfigured to receive electric power from the electric powertransmission apparatus, wherein the electric power transmissionapparatus or the electric power receiving apparatus includes a resonancecircuit including at least a coil and a capacitor, the coil being usedfor electric power transmission or electric power reception, a detectionunit configured to measure a Q value of the resonance circuit, a circuitswitching unit configured to switch a circuit configuration of theresonance circuit between electric power supply time and Q valuemeasurement time, and a control unit configured to control switching bythe circuit switching unit.

[40] A detection method comprising: switching, at the time of Q valuemeasurement, a circuit configuration of a resonance circuit from acircuit configuration at the time of electric power supply, theresonance circuit including at least a coil and a capacitor, theresonance circuit being included in an electric power transmissionapparatus or an electric power receiving apparatus forming a non-contactelectric power transmission system; and measuring a Q value of theresonance circuit after the circuit configuration of the resonancecircuit is switched.

The series of processing in the above-mentioned exemplary embodimentscan be performed by hardware and can also be performed by software. Whenthe series of processing is to be performed by software, it can beperformed by a computer in which a program constituting the software isinstalled into specialized hardware or by a computer in which programsfor performing various programs are installed. For example, a programforming desired software may be installed into a general-purposepersonal computer, whereby the program is executed.

Furthermore, a recording medium having recorded thereon program code ofsoftware for realizing the functions of the above-described embodimentsmay be supplied to a system or an apparatus. Furthermore, when thecomputer (or a control device, such as a CPU) of the system or theapparatus reads the program code stored on a recording medium andexecutes the program code, of course, the functions can be realized.

For recording media for supplying program code in this case, forexample, a flexible disk, a hard disk, an optical disc, amagneto-optical disc, a CD-ROM, a CD-R, a magnetic tape, a non-volatilememory card, or a ROM can be used.

Furthermore, by executing the program code read by the computer, thefunctions of the above-described embodiment are realized. Additionally,an OS or the like, which runs on the computer, performs part or thewhole of the actual processing on the basis of the instructions of theprogram code. A case in which the processing realizes the functions ofthe above-described embodiments is also included.

In this specification, processing steps describing time-seriesprocessing may include, as well as processes executed in time series inaccordance with the written order, processes executed in parallel orindividually (for example, parallel processes or object-basedprocesses), which may not necessarily be executed in time series.

As has been described above, the present disclosure is not limited tothe above-described embodiments. Of course, other various modificationsand application examples can be configured without departing from thegist described in the claims.

That is, since the embodiments described above are preferred examples ofthe present disclosure, various technically preferable restrictions havebeen added. However, the technical scope of the present disclosure isnot limited to these embodiments unless otherwise indicated in thefollowing description as limiting the present disclosure. For example,the used materials, the amounts thereof used, the processing timeperiod, the processing sequence, numerical conditions of parameters, andthe like, which are given in the foregoing description, are onlypreferred examples, and the dimensions, shapes, and arrangementrelationship, which are used for description in each figure, areapproximate.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-162589 filed in theJapan Patent Office on Jul. 25, 2011, the entire contents of which arehereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A power transmission device comprising: a resonance circuit includinga coil and a capacitor; detection circuitry configured to measure afirst Q-value of the resonance circuit; and control circuitry configuredto supply an alternating current to the resonance circuit for themeasurement of the Q-value and to control the detection circuitry tomeasure the first Q-value, in a state where the resonance circuit is nottransmitting power.
 2. The power transmission device according to claim1, wherein the detection circuitry includes determination circuitryconfigured to compare the first Q-value with a threshold value todetermine whether a foreign object is in a space affecting the powertransmission.
 3. The power transmission device according to claim 2,wherein the threshold value is based on information received from apower reception device in communication with the power transmissiondevice.
 4. The power transmission device according to claim 2, whereinthe threshold value is a second Q-value that is based on a measuredvalue received from the power reception device.
 5. The powertransmission device according to claim 2, wherein, in a case where thefirst Q-value is higher than or equal to the threshold value, the powertransmission device transmits power to a power reception device.
 6. Thepower transmission device according to claim 2, wherein, in a case wherethe first Q-value is less than the threshold value, the powertransmission device does not transmit power to a power reception device.7. The power transmission device according to claim 2, furthercomprising communication circuitry configured to communicate with apower reception device.
 8. The power transmission device according toclaim 6, wherein the communication circuitry is configured to receive aninstruction to determine whether the foreign object is in the spaceaffecting the power transmission.
 9. The power transmission deviceaccording to claim 1, wherein the detection circuitry is configured toobtain a first voltage at a first node of the resonance circuit and asecond voltage at a second node of the resonance circuit, wherein thecapacitor is connected between the first node and the second node, andthe detection circuitry includes: computing circuitry configured tocompute the first Q-value based on the first voltage and the secondvoltage, and determination circuitry configured to compare the firstQ-value with a threshold value to determine whether a foreign object isin a space affecting the power transmission.
 10. The power transmissiondevice according to claim 9, wherein the detection circuitry furthercomprises: a first analog-to-digital converter configured to convert thefirst voltage to a first digital signal, and to output the first digitalsignal to the computing circuitry; and a second analog-to-digitalconverter configured to convert the second voltage to a second digitalsignal, and to output the second digital signal to the computingcircuitry.
 11. The power transmission device according to claim 9,further comprising a memory configured to store the threshold value. 12.The power transmission device according to claim 9, wherein the firstQ-value is a ratio of the first voltage to the second voltage.
 13. Thepower transmission device according to claim 1, wherein the powertransmission is a wireless power transmission.
 14. An electronicapparatus comprising the power transmission device according to claim 1.15. A power reception device comprising: a resonance circuit including acoil and a capacitor; detection circuitry configured to measure aQ-value of the resonance circuit; and control circuitry configured tosupply an alternating current to the resonance circuit for themeasurement of the Q-value and to control the detection circuitry tomeasure the Q-value, in a state where the resonance circuit is notreceiving power.
 16. The power reception device according to claim 15,wherein the detection circuitry includes determination circuitryconfigured to compare the Q-value with a threshold value to determinewhether a foreign object is in a space affecting the power reception.17. An electronic apparatus comprising the power reception deviceaccording to claim
 15. 18. A power transfer system comprising: a powertransmission device; and a power reception device, wherein one or bothof the power transmission device and the power reception devicerespectively include: a resonance circuit including a coil and acapacitor, detection circuitry configured to measure a Q-value of theresonance circuit, and control circuitry configured to supply analternating current to the resonance circuit for the measurement of theQ-value and to control the detection circuitry to measure the Q-value,in a state where the resonance circuit is not transferring power. 19.The power transfer system according to claim 18, wherein the powertransmission device includes the resonance circuit, the detectioncircuitry, and the control circuitry.
 20. The power transfer systemaccording to claim 19, wherein the detection circuit includes adetermination circuit configured to compare the Q-value with a thresholdvalue to determine whether a foreign object is in a space affecting thepower transmission.